Wiring board and method for manufacturing the same

ABSTRACT

A wiring board having an insulation layer, and a buildup structure formed on the insulation layer and including insulation layers. The insulation layer and the buildup structure form a board structure in which a cavity portion having an opening on a surface of the buildup structure on the opposite side of the insulation layer is formed. The cavity portion is extending through one or more of the insulation layers in the buildup structure and has a groove portion formed on the bottom surface of the cavity portion along a wall surface of the cavity portion. The board structure composed of the insulation layer and the buildup structure has a pad formed on the bottom surface of the cavity portion in a position farther from the wall surface of the cavity portion than the groove portion.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of and claims the benefit ofpriority to U.S. application Ser. No. 13/249,507, filed Sep. 30, 2011,which claims the benefit of priority to U.S. Application No. 61/432,322,filed Jan. 13, 2011. The entire contents of these applications areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a wiring board and its manufacturingmethod.

2. Discussion of the Background

Japanese Laid-Open Patent Publication No. 2007-266196 describes a wiringboard in which a cavity is formed to open toward one side and there aremultiple pads on the bottom surface of the cavity, and a method formanufacturing such a wiring board. The contents of Japanese Laid-OpenPatent Publication No. 2007-266196 are incorporated herein by referencein their entirety in the present application.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a wiring boardincludes an insulation layer, and a buildup structure formed on theinsulation layer and including insulation layers. The insulation layerand the buildup structure form a board structure in which a cavityportion having an opening on a surface of the buildup structure on theopposite side of the insulation layer is formed. The cavity portion isextending through one or more of the insulation layers in the buildupstructure and has a groove portion formed on the bottom surface of thecavity portion along a wall surface of the cavity portion. The boardstructure composed of the insulation layer and the buildup structure hasa pad formed on the bottom surface of the cavity portion in a positionfarther from the wall surface of the cavity portion than the grooveportion.

According to another aspect of the present invention, a method formanufacturing a wiring board includes preparing an insulation layerhaving a conductive layer including a pad formed on a surface of theinsulation layer, covering the pad with a mask layer which is separablefrom the insulation layer and is substantially corresponding to thebottom surface of a cavity portion, forming on the insulation layer, theconductive layer and the mask layer a buildup structure havinginsulation layers, irradiating laser on a surface of the buildupstructure on the opposite side of the insulation layer substantiallyalong the shape of the mask layer such that the laser forms a separableportion including the mask layer in the buildup structure and a grooveportion in the insulation layer substantially along the shape of themask layer, and removing the separable portion formed in the buildupstructure such that the cavity portion having the groove portion on thesurface of the insulation layer is formed and the pad is exposed on thebottom surface of the cavity portion in the position farther from thewall surface of the cavity portion than the groove portion.

According to yet another aspect of the present invention, a method formanufacturing a wiring board includes forming a board structure havingan insulation layer, a buildup structure formed on the insulation layerand a pad formed in the board structure, the buildup structure includinginsulation layers, and forming a cavity portion in the board structuresuch that the cavity portion has an opening on a surface of the buildupstructure on the opposite side of the insulation layer, the cavityportion is extending through one or more of the insulation layers in thebuildup structure, the cavity portion has a groove portion formed on thebottom surface of the cavity portion along a wall surface of the cavityportion, and the pad formed in the board structure is exposed on thebottom surface of the cavity portion in the position farther from thewall surface of the cavity portion than the groove portion. The formingof the board structure includes covering the pad with a separable masklayer which is substantially corresponding to the bottom surface of thecavity portion. The forming of the cavity portion in the board structureincludes irradiating laser on the surface of the buildup structuresubstantially along the shape of the mask layer such that the laserforms a separable portion including the separable mask layer in thebuildup structure and a groove portion in the bottom surface of thecavity portion substantially along the shape of the mask layer andremoving the separable portion formed in the buildup structure such thatthe cavity portion having the groove portion is formed and the pad isexposed in the cavity portion formed in the board structure.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view showing a wiring board according to anembodiment of the present invention;

FIG. 2 is a plan view showing how cavities and grooves are formed in awiring board according to the embodiment of the present invention;

FIG. 3A is a magnified plan view of a cavity in the wiring board shownin FIG. 2;

FIG. 3B is a magnified view of the connection section shown in FIG. 3A;

FIG. 4 is a view showing how solder resists are formed in a wiring boardaccording to the embodiment of the present invention;

FIG. 5 is a view showing an electrode in a wiring board according to theembodiment of the present invention;

FIG. 6A is a view showing an example in which an electronic component ismounted on a wiring board according to the embodiment of the presentinvention;

FIG. 6B is a plan view of the wiring board shown in FIG. 6A;

FIG. 7A is a view showing a state in which an electronic component ismounted on a wiring board where no groove is formed on the bottomsurface of a cavity;

FIG. 7B is a view showing a state in which an electronic component ismounted on a wiring board according to the embodiment of the presentinvention;

FIG. 8 is a flowchart showing a method for manufacturing a wiring boardaccording to the embodiment of the present invention;

FIG. 9 is a view to illustrate a step for preparing a core substrate (aninsulation layer where conductive layers are formed on its mainsurfaces) in the manufacturing method shown in FIG. 8;

FIG. 10 is a view to illustrate a step for forming inner-layer solderresist in the manufacturing method shown in FIG. 8;

FIG. 11 is a view to illustrate a step for forming a mask in themanufacturing method shown in FIG. 8;

FIG. 12A is a view to illustrate a first step for buildup in themanufacturing method shown in FIG. 8;

FIG. 12B is a view to illustrate a second step for buildup in themanufacturing method shown in FIG. 8;

FIG. 13 is a view to illustrate a third step for buildup in themanufacturing method shown in FIG. 8;

FIG. 14 is a view to illustrate a step for forming outer-layer solderresists in the manufacturing method shown in FIG. 8;

FIG. 15A is a view to illustrate a step for irradiating a laser in themanufacturing method shown in FIG. 8;

FIG. 15B is a magnified view of the connection section during the stepfor irradiating a laser in the manufacturing method shown in FIG. 8;

FIG. 16 is a view showing a groove formed by irradiating a laser in themanufacturing method shown in FIG. 8;

FIG. 17 is a view to illustrate a step for forming a cavity in themanufacturing method shown in FIG. 8;

FIG. 18 is a view showing a cavity shaped differently in a wiring boardaccording to the embodiment of the present invention;

FIG. 19 is a view showing an alternative example in which a groove isformed intermittently in a wiring board according to the embodiment ofthe present invention;

FIG. 20 is a view showing yet another alternative example in which agroove is formed only along portions of the wall surfaces of a cavity ina wiring board according to the embodiment of the present invention;

FIG. 21 is a view showing yet another alternative example in which a padis positioned in a portion corresponding to a break in the ring formedby a groove in a wiring board according to the embodiment of the presentinvention;

FIG. 22 is a view showing yet another alternative example in which theangle between a groove and a conductive pattern in the connectionsection is either acute or obtuse in a wiring board according to theembodiment of the present invention;

FIG. 23A is a view showing a first alternative example in which thedepth of a cavity is different in a wiring board according to theembodiment of the present invention;

FIG. 23B is a view showing a second alternative example in which thedepth of a cavity is different in a wiring board according to theembodiment of the present invention;

FIG. 24A is a view showing a first alternative example in which a groovehas a different cross-sectional shape in a wiring board according to theembodiment of the present invention;

FIG. 24B is a view showing a second alternative example in which agroove has a different cross-sectional shape in a wiring board accordingto the embodiment of the present invention;

FIG. 24C is a view showing a third alternative example in which a groovehas a different cross-sectional shape in a wiring board according to theembodiment of the present invention;

FIG. 24D is a view showing a fourth alternative example in which agroove has a different cross-sectional shape in a wiring board accordingto the embodiment of the present invention;

FIG. 25 is a view showing an alternative example in which a groove has adifferent planar shape in a wiring board according to the embodiment ofthe present invention;

FIG. 26 is a view showing an alternative example in which an electroniccomponent is mounted in a different way in a wiring board according tothe embodiment of the present invention;

FIG. 27 is a view showing another alternative example in which a wiringboard instead of an electronic component is mounted in a wiring boardaccording to the embodiment of the present invention;

FIG. 28 is a view showing a wiring board according to another embodimentof the present invention where the terminal pitch of the pads formed onthe bottom surface of a cavity is widened toward the outer layer;

FIG. 29 is a view showing a flex-rigid wiring board according to yetanother embodiment of the present invention; and

FIG. 30 is a view showing a single-sided wiring board according to yetanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

In the drawings, arrows (Z1, Z2) each indicate a lamination direction ina wiring board corresponding to a direction along a normal line (or adirection of the thickness of a core substrate) to the main surfaces(upper and lower surfaces) of the wiring board. On the other hand,arrows (X1, X2) and (Y1, Y2) each indicate a direction perpendicular toa lamination direction (or a direction to a side of each layer). Themain surfaces of the wiring board are on the X-Y plane. Side surfaces ofthe wiring board are on the X-Z plane or the Y-Z plane.

Two main surfaces facing opposite directions of a normal line arereferred to as a first surface (the Z1-side surface) and a secondsurface (the Z2-side surface). In lamination directions, the side closerto the core is referred to as a lower layer (or inner-layer side), andthe side farther from the core is referred to as an upper layer (orouter-layer side). On the X-Y plane, a side farther from the cavity (itsgravity center, in particular) is referred to as an outer side, and aside closer to the cavity is referred to as an inner side. “Directly on”means in direction Z (the Z1 side or the Z2 side).

Except for a plain conductive layer, a conductive layer is formed with aconductive portion (hereinafter referred to as a conductive pattern) anda non-conductive portion. A conductive layer may include a conductivepattern that forms an electric circuit such as wiring (includingground), a pad and a land, or it may include a plain conductive patternthat does not form an electric circuit. Alternatively, in a wiring boardwith a built-in electronic component or another wiring board, theelectrodes of the electronic component or the pads of the other wiringboard may be positioned so that they are included in a conductive layerof the wiring board. Such pads include external connection terminals,via connection terminals and the like.

Opening portions include holes, grooves, notches, slits and so forth.Holes are not limited to penetrating holes, and non-penetrating holesare also referred to as holes. Holes include via holes and throughholes. Hereinafter, the conductor formed in a via hole (its wall andbottom surfaces) is referred to as a via conductor, and the conductorformed in a through hole (its wall surface) is referred to as athrough-hole conductor.

Plating includes wet plating such as electrolytic plating as well as dryplating such as PVD (physical vapor deposition) and CVD (chemical vapordeposition).

“Preparing” includes situations in which material and components arepurchased and manufactured accordingly as well as situations in whichfinished products are purchased and used accordingly.

“Surround” includes situations in which a ring without any breaksurrounds a region completely (see FIG. 18), along with situations inwhich a ring with a partial break surrounds a region (see FIG. 2˜FIG.3B), and other situations in which a ring formed with a broken linesurrounds a region (see FIG. 19) and the like. A ring means a planarshape formed by connecting both ends of a line; and rings include notonly a circle but also polygons.

Wiring board 100 of the present embodiment is a printed wiring board. Asshown in FIG. 1, wiring board 100 has wiring board 10, insulation layers(20 a, 30 a, 40 a, 50 a, 60 a, 70 a), conductive layers (21, 31, 41, 51,61, 71) and via conductors (22, 32, 42, 52, 62, 72). Wiring board 10 isthe core substrate for wiring board 100. Hereinafter, one of the upperand lower surfaces (two main surfaces) of wiring board 10 is referred toas first surface (F1) and the other as second surface (F2).

Wiring board 10 has insulation layer (10 a), conductive layers (11 a, 11b) and via conductors 12. Conductive layer (11 a) is formed on thefirst-surface (F1) side of insulation layer (10 a), and conductive layer(11 b) is formed on the second-surface (F2) side of insulation layer (10a). Via holes (12 a) that penetrate through insulation layer (10 a) areformed in insulation layer (10 a). Via conductors 12 are formed byfilling, for example, copper plating in via holes (12 a). Multiple viaconductors 12 formed in insulation layer (10 a) include via conductors121 that form filled-stack structure “S” and via conductors 122 that areelectrically connected to pads 101 in cavity (R1). Pads 101 are formeddirectly on via conductors 122 and are directly connected to viaconductors 122.

Buildup section 30 (laminated section) is formed on the first-surface(F1) side of wiring board 10, and buildup section 20 is formed on thesecond-surface (F2) side of wiring board 10. Buildup section 30 isformed with insulation layers (30 a, 50 a, 70 a), conductive layers (31,51, 71) and solder resist 81. Three insulation layers (30 a, 50 a, 70 a)and three conductive layers (31, 51, 71) are alternately laminated, andlowermost insulation layer (30 a) is formed on first surface (F1) ofwiring board 10 and solder resist 81 is formed on the outermost layer ofthe first-surface (F1) side. Also, buildup section 20 is formed withinsulation layers (20 a, 40 a, 60 a), conductive layers (21, 41, 61) andsolder resist 82. Three insulation layers (20 a, 40 a, 60 a) and threeconductive layers (21, 41, 61) are alternately laminated, and lowermostinsulation layer (20 a) is formed on second surface (F2) of wiring board10 and solder resist 82 is formed on the outermost layer of thesecond-surface (F2) side. Insulation layers (20 a, 30 a, 40 a, 50 a, 60a, 70 a) each correspond to an interlayer resin insulation layer.Instead of solder resists (81, 82), coverlays may also be used.

Conductive layer 71 becomes the outermost conductive layer on thefirst-surface (F1) side, and conductive layer 61 becomes the outermostconductive layer on the second-surface (F2) side. Solder resists (81,82) are formed on conductive layers (71, 61) respectively. However,since opening portions (81 a, 82 a) are formed in solder resists (81,82) respectively, predetermined spots of conductive layer 71 (spotscorresponding to opening portions 81 a) are exposed without beingcovered by solder resist 81 and become pads (P1). Also, predeterminedspots of conductive layer 61 (spots corresponding to opening portions 82a) become pads (P2). Pads (P1) become external connection terminals formounting an electronic component, for example; and pads (P2) becomeexternal connection terminals for electrical connection with anotherwiring board, for example. However, the uses of pads (P1, P2) are notlimited to those, and they may be used for any other purposes.

Insulation layer (10 a) is made of a rigid substrate, for example.Insulation layer (10 a) is made by, for example, impregnating glasscloth (core material) with epoxy resin (hereinafter referred to asglass-epoxy resin). The core material is a material whose thermalexpansion coefficient is smaller than the primary material (epoxy resinin the present embodiment). As for such a core material, inorganicmaterial such as glass fiber (glass cloth or glass non-woven fabric, forexample), aramid fiber (aramid non-woven fabric, for example) or silicafiller is preferred. However, the shape, thickness, material and thelike of insulation layer (10 a) are basically selected freely. Forexample, instead of epoxy resin, the following may be used: polyesterresin, bismaleimide triazine resin (BT resin), imide resin (polyimide),phenol resin, allyl polyphenylene ether resin (A-PPE resin) and thelike. Insulation layer (10 a) may be formed with multiple layers made ofdifferent materials. Insulation layer (10 a) may also be made of aflexible substrate, for example (see later-described FIG. 29).

Insulation layers (20 a, 30 a, 40 a, 50 a, 60 a, 70 a) are each made ofepoxy resin, for example. Insulation layers (20 a) and the like are madeof resin without a core material in the present embodiment. However,insulation layers (20 a) and the like are not limited to such, and theshape, thickness, material and the like are basically selected freely.For example, it is optional that insulation layers (20 a) and the likein buildup sections (20, 30) also contain a core material.

Conductive layers (11 a, 11 b, 21, 31, 41, 51, 61, 71) each have atwo-layer structure of copper foil and copper plating, for example. Thedetailed structure of conductive layer (11 a) (especially pads 101),conductive layer 71 (especially pads P1) and conductive layer 61(especially pads P2) is described later (see FIG. 5). However, thematerial for such conductive layer (11 a) and others is not limited tosuch and may be selected freely.

Via conductors 12 are made of copper plating, for example. The shape ofvia conductors 12 is a tapered column (truncated cone) with a diameterincreasing toward the Z1 side, for example. However, the material andthe shape of via conductors 12 are not limited to such and may beselected freely.

Via holes (22 a, 32 a, 42 a, 52 a, 62 a, 72 a) are formed in insulationlayers (20 a, 30 a, 40 a, 50 a, 60 a, 70 a) respectively. Via conductors(22, 32, 42, 52, 62, 72) are formed respectively by filling copperplating, for example, in via holes (22 a) and the like. Via conductors22 and the like are each shaped as a tapered column (truncated cone)with a diameter increasing toward their respective upper layer, forexample. However, the material and shape of via conductors 22 and thelike are not limited to such and may be selected freely.

In wiring board 100, filled-stack structure “S” is extended in directionZ by laminating via conductor 12 (especially via conductor 121) and viaconductors (22, 32, 42, 52, 62, 72) (each is a filled conductor) on bothsides of wiring board 10 (the first-surface (F1) side and thesecond-surface (F2) side). Adjacent via conductors are adhered (incontact) and are electrically connected to each other. Filled-stackstructure “S” electrically connects conductive layers on both surfacesof wiring board 100, namely, conductive layer 71 on the first-surface(F1) side and conductive layer 61 on the second-surface (F2) side.

Filled-stack structure “S” is a so-called full-stack structure wherefilled conductors throughout the layers are laminated. Thus, ensuringwiring space is easy, and the design flexibility of wiring patternsincreases. Also, since wiring in direction X or direction Y is omitted,the wiring length is reduced in interlayer connections. The position andthe number of filled-stack structures “S” may be selected freely. Forexample, there may be multiple filled-stack structures “S.”

Through holes (111 a), which penetrate through wiring board 100, areformed in wiring board 100, and through-hole conductors 111 are formedby forming copper plating, for example, on wall surfaces of throughholes (111 a).

In the present embodiment, cavity (R1), which opens on one side ofwiring board 100 (the first-surface (F1) side), is formed in buildupsection 30 as shown in FIG. 1. Also, as shown in FIG. 2, wiring board100 of the present embodiment has cavities (R2, R3), which open on oneside of wiring board 100 (the first-surface (F1) side), in addition tocavity (R1). Wall surfaces (F12, F22, F32) of cavities (R1, R2, R3)correspond to side surfaces of buildup section 30. Cavities (R1, R2, R3)are shaped to be substantially rectangular. The number of cavitiesformed in wiring board 100 is not limited to three, and any other numbermay be employed. Also, the shape of cavities is selected freely (seelater-described FIG. 18).

Cavity (R1) is formed to be a hole. Cavity (R2) is formed to be a notch.The number of wall surfaces of cavity (R2) is three and one side is leftopen. In addition, cavity (R3) is formed by connecting holes (throughholes 111 a) that penetrate through wiring board 100 and a hole thatpenetrates only through buildup section 30 (see cavity (R1) in FIG. 1).

On bottom surface (F11) of cavity (R1), groove (T1) shaped as arectangular ring, for example, is formed substantially along all thewall surfaces (F12) (four sides) of cavity (R1). Groove (T1) is formedcontinuously except for later-described connection section (R13) (seeFIGS. 3A and 3B). In the present embodiment, groove (T1) is shaped as arectangular ring where there is substantially no break, and pads 101 arepositioned in a partial region of bottom surface (F11) surrounded bygroove (T1). Also, on bottom surface (F21) of cavity (R2), groove (T2)is formed entirely along wall surfaces (F22) (three sides) of cavity(R2). In the present embodiment, groove (T2) is formed in a “U” shapeand pads 102 are positioned in a partial region of bottom surface (F21)surrounded by groove (T2). In addition, on bottom surface (F31) ofcavity (R3), groove (T3) is formed along wall surfaces (F32) of cavity(R3) (excluding portions of through holes (111 a)). Groove (T3) isinterrupted by through holes (111 a). In the present embodiment, groove(T3) is shaped as a rectangular ring having breaks, and pads 103 arepositioned in a partial region of bottom surface (F31) surrounded bygroove (T3). In the present embodiment, grooves (T1, T2, T3) are formedin insulation layer (10 a) (a rigid substrate containing a corematerial). Therefore, because of the core material, it is easier toadjust the depths of grooves (T1, T2, T3). Also, surface flatness iseasily ensured when forming pads and solder resist.

Groove (T1) is formed near wall surfaces (F12) of cavity (R1); groove(T2) is formed near wall surfaces (F22) of cavity (R2); and groove (T3)is formed near wall surfaces (F32) of cavity (R3). Wiring board 100 hasthe following: pads 101 which are positioned on bottom surface (F11) ofcavity (R1) farther from wall surfaces (F12) than groove (T1) is; pads102 which are positioned on bottom surface (F21) of cavity (R2) fartherfrom wall surfaces (F22) than groove (T2) is; and pads 103 which arepositioned on bottom surface (F31) of cavity (R3) farther from wallsurfaces (F32) than groove (T3) is.

A magnified view of cavity (R1) is shown in FIG. 3A. Hereinafter, of theentire bottom surface (F11) of cavity (R1), a region where groove (T1)is formed is referred to as groove section (R11), and the rest asnon-groove section (R12). Groove section (R11) is positioned mainlyalong the periphery of cavity (R1), and non-groove section (R12) ispositioned mainly inside groove section (R11).

As shown in FIG. 3A, wiring board 100 has pads 101 on non-groove section(R12) surrounded by groove (T1). Pads 101 include multiple pads (101 a)and multiple pads (101 b). Wiring board 100 has multiple conductivepatterns (101 c) electrically connected to pads (101 b). Pads 101 andconductive patterns (101 c) are included in conductive layer (11 a). Inthe present embodiment, conductive patterns (101 c) each correspond towiring that electrically connects a terminal in cavity (R1) (pad 101 b)and another circuit outside cavity (R1).

Cavity (R1) reaches first surface (F1) of wiring board 10 from a surfaceof wiring board 100. The depth of cavity (R1) is preferred to bedetermined according to the depth of the electronic component to beaccommodated in cavity (R1). However, if cavity (R1) is shallower, it iseasier to reduce warping in wiring board 100.

In the present embodiment, the planar surface of groove (T1) (on the X-Yplane) is shaped straight with a substantially uniform width. Inaddition, a cross section of groove (T1) (the cross sectionperpendicular to the longitudinal direction) in the present embodimentis shaped to have four sides that intersect at substantially rightangles. Namely, the width of groove (T1) is constant regardless of itsdepth. The depth of groove (T1) is approximately 20 μm, for example.Also, width (D2) of groove (T1) (groove section R11) is approximately100 μm, for example. However, the shape and measurements of groove (T1)are determined freely (see later-described FIGS. 24A-25).

Widths (D11, D12) of non-groove section (R12) surrounded by groove (T1)are each preferred to be determined according to the size of a componentto be accommodated in cavity (R1).

In addition, in the present embodiment, conductive patterns (101 c) areeach formed in a linear shape that extends in direction X. Suchconductive patterns (101 c) are formed substantially parallel to eachother in the vicinity of each other. The L/S (width/distance) of suchconductive patterns (101 c) are each set at approximately 50μm/approximately 50 μm, for example.

As shown in FIG. 3B (magnified view of FIG. 3A), conductive patterns(101 c) are each formed in non-groove section (R12). Namely, conductivepatterns (101 c) are each formed in a region on bottom surface (F11) ofcavity (R1) where groove (T1) is not formed. Then, conductive patterns(101 c) extended in direction X are each formed to cross groove (T1),which runs along direction Y. By doing so, portions of groove (T1) andconductive patterns (101 c) are alternately positioned in theintersection (hereinafter referred to as connection section (R13)). Inthe present embodiment, portions of groove (T1) and conductive patterns(101 c) are alternately positioned along direction Y. Namely, groove(T1) is formed intermittently in connection section (R13). Also, groove(T1) and conductive patterns (101 c) make an angle of approximately 90degrees in connection section (R13). However, such is not the onlyoption, and the angle at which conductive patterns (101 c) cross groove(T1) may be determined freely (see later-described FIG. 22).

In the present embodiment, since multiple conductive patterns (101 c)are positioned to be separated by groove (T1), short circuiting betweenconductive patterns (101 c) caused by a solder bridge or the like seldomoccurs. As a result, wiring is easily set to be finer.

As shown in FIGS. 1 and 4, in addition to solder resists (81, 82)(outer-layer solder resists) formed on their respective main surfaces),wiring board 100 has solder resist 83 (inner-layer solder resist) onnon-groove section (R12) (excluding connection section R13) on bottomsurface (F11) of cavity (R1). Solder resist 83 has opening portions (83a) and pads 101 are exposed through opening portions (83 a).

In cavity (R1) of the present invention, solder resist is not formed ongroove section (R11) of bottom surface (F11) nor on non-groove section(R12) of connection section (R13). Namely, as shown in FIG. 4,conductive patterns (101 c) are exposed in non-groove section (R12) ofconnection section (R13). However, since groove (T1) is formed betweenconductive patterns (101 c) in the present embodiment (see FIG. 3),short circuiting between conductive patterns (101 c) is suppressed bygroove (T1).

Pads 101 formed on the bottom surface of cavity (R1), pads (P1) formedon a main surface outside cavity (R1) (main surface on the first-surface(F1) side) and pads (P2) formed on the opposite main surface (mainsurface on the second-surface (F2) side) have anticorrosion layers(1013, P13, P23) respectively as shown in FIG. 5. In particular, pads101 have a triple-layer structure in which copper foil 1011, platedlayer 1012 and anticorrosion layer 1013 are laminated in that order fromthe lowest layer. Also, portions of conductive patterns (101 c) exposedin non-groove section (R12) of connection section (R13) (see FIG. 4)have a triple-layer structure of copper foil 1011, plated layer 1012 andanticorrosion layer 1013. Pads (P1) have a triple-layer structure inwhich copper foil (P11), plated layer (P12) and anticorrosion layer(P13) are laminated in that order from the lowest layer. Pads (P2) havea triple-layer structure in which copper foil (P21), plated layer (P22)and anticorrosion layer (P23) are laminated in that order from thelowest layer. Anticorrosion layers (1013, P13, P23) are each made of thesame material (such as Ni/Au film or OSP film) and are formed byelectrolytic plating or OSP treatment or the like. Here, conductivelayers (11 a, 61, 71) may have an anticorrosion layer only on theexposed surfaces (such as pad surfaces), or they may have ananticorrosion layer on their respective entire surface.

As shown in FIG. 6A, for example, electronic component 200 withelectrodes (200 a) is accommodated in cavity (R1). In addition, solder(200 b) is formed on pads 101 in cavity (R1) (in particular onanticorrosion layer 1013 shown in FIG. 5). Then, pads 101 and electroniccomponent 200 are electrically connected to each other through solder(200 b). Here, what is electrically connected to pads 101 is not limitedto an electronic component, and may be selected freely (seelater-described FIG. 27).

As shown in FIG. 6B, for example, electronic component 200 is positionedso that its side surfaces (all four sides) are entirely positioned ongroove section (R11). Space (D10) between wall surfaces (F12) of cavity(R1) and electronic component 200 (½ of clearance) is approximately 20mm, for example. However, positioning and measurements of electroniccomponent 200 are not limited to such and may be determined freely (seelater-described FIG. 26).

According to wiring board 100 of the present embodiment, electricalconnection reliability at pads 101 is enhanced without increasing space(D 10). As a result, it is easier to reduce space (D10) (or clearance)between wall surfaces (F12) of cavity (R1) and electronic component 200.The reasons for that are described in the following by referring toFIGS. 7A and 7B.

FIG. 7A shows a wiring board where groove (T1) is not formed on bottomsurface (F11) of cavity (R1). As shown in FIG. 7A, skirt portion (H1)tends to be formed by the resin in buildup section 30 being squeezed tothe side of cavity (R1) in such a wiring board. Of the entire bottomsurface (F11) of cavity (R1), a portion where skirt portion (H1) isformed swells and rises. Hereinafter, of the entire bottom surface (F11)of cavity (R1), the region where skirt portion (H1) is formed isreferred to as protruding portion (R101) and the rest is referred to asnon-protruding portion (R102).

Since skirt portion (H1) tends to be formed with various heights alongwall surfaces (F12) of cavity (R1), the flatness of bottom surface (F11)of cavity (R1) tends to decrease near wall surfaces (F12) of cavity (R1)in a wiring board shown in FIG. 7A. As a result, when mountingelectronic component 200 on pads (not shown in the drawing) formed innon-protruding portion (R102) (see pads 101 shown in FIGS. 1 and 2),electronic component 200 makes contact with skirt portion (H1), causingvarious distances between electronic component 200 and the mountingsurface (non-protruding portion R102). Accordingly, there is a concernthat electronic component 200 may be mounted while being positioned atan incline. Then, as a result, the electrical connection reliabilitytends to decrease at the pads formed on bottom surface (F11) of cavity(R1).

To solve the above problems, it may be an option to increase space (D10)(or clearance) between wall surfaces (F12) of cavity (R1) and electroniccomponent 200. However, if space (D10) is increased (namely, cavity (R1)is enlarged), another concern may arise such that the area of the mainsurface outside cavity (R1) is reduced, and space for forming wiringbecomes smaller.

For that matter, in wiring board 100 of the present embodiment shown inFIG. 7B, groove (T1) is formed along wall surfaces (F12) of cavity (R1)on bottom surface (F11) of cavity (R1). Then, pads 101 (see FIGS. 1, 2)are formed in positions (in non-groove section (R12)) on bottom surface(F11) of cavity (R1) which are farther from wall surfaces (F12) thangroove (T1) is. More specifically, groove (T1) is formed near wallsurfaces (F12) of cavity (R1), and wall surfaces (F12) of cavity (R1)and pads 101 are separated by groove (T1). Accordingly, skirt portion(H1) (protruding portion) is seldom formed near wall surfaces (F12) ofcavity (R1), and it is easier to make the distance constant betweenelectronic component 200 and the mounting surface (non-groove section(R12)) as shown in FIG. 7B. As a result, the electrical connectionreliability at pads 101 is enhanced. Since space (D10) is not requiredto be enlarged in such a structure, it is easier to decrease space (D10)(or clearance) between wall surfaces (F12) of cavity (R1) and electroniccomponent 200. As a result, it is easier to ensure space for formingwiring on the main surface outside cavity (R1).

The above wiring board 100 is manufactured by the process shown in FIG.8, for example.

In step (S11), wiring board 10 is prepared. Wiring board 10 hasinsulation layer (10 a), conductive layers (11 a, 11 b) and viaconductors 12. Via conductors 12 are filled conductors.

Conductive layer (11 a) is formed on a main surface of insulation layer(10 a) and conductive layer (11 b) is formed on the other main surfaceof insulation layer (10 a). However, conductive layer (11 a) does nothave conductive patterns on the region corresponding to groove section(R11) on the main surface (first surface (F1)) of insulation layer (10a) (see FIG. 3A). As a result, insulation layer (10 a) is exposed in theregion corresponding to groove section (R11).

For example, wiring board 10 may be formed as follows: using adouble-sided copper-clad laminate as a starting material; forming viaholes in the laminate by a laser, for example; performing copper panelplating; and patterning conductive layers on both surfaces usinglithographic technology, for example. Insulation layer (10 a) is made ofcompletely cured glass-epoxy resin, for example.

In step (S12) of FIG. 8, solder resist 83 for pads 101 (inner-layersolder resist) is formed on the region corresponding to bottom surface(F11) of cavity (R1) (especially non-groove section (R12)) as shown inFIG. 10, for example. Solder resist 83 may be formed by screen printing,spray coating, roll coating, lamination or the like. Anticorrosion layer1013 is not formed on pads 101 at this stage. In the present embodiment,anticorrosion layer 1013 of pads 101 is formed simultaneously withanticorrosion layers (P13, P23) of pads (P1, P2). By doing so,manufacturing efficiency is improved.

In step (S13) of FIG. 8, mask 1001 is formed on solder resist 83 asshown in FIG. 11, for example. Mask 1001 has substantially the sameouter shape (on the X-Y plane) as that of solder resist 83, for example.

In step (S14) of FIG. 8, outer-layer solder resists are formed afterbuildup is performed on both surfaces of wiring board 10. Accordingly,buildup sections (30, 20) are formed respectively on first surface (F1)and second surface (F2) of wiring board 10.

More specifically, after mask 1001 is formed, copper foil 1002,insulation layer (20 a), wiring board 10, insulation layer (30 a) andcopper foil 1003 are positioned in that order from the second-surface(F2) side as shown in FIG. 12A, for example. Here, by positioninginsulation layer (30 a) on the sides of mask 1001 and by making theheight of insulation layer (30 a) substantially the same as the heightof mask 1001, a substantially flat surface is formed by their mainsurfaces. Then, copper foil 1003 is formed on the substantially flatsurface. Wiring board 10 is sandwiched by insulation layers (20 a, 30a), which are then sandwiched by copper foil 1002 and copper foil 1003.At this stage, insulation layers (20 a, 30 a) are prepreg (semi-curedadhesive sheets). However, RCF (resin-coated copper foil) or the likemay also be used instead of prepreg.

The above laminate is thermal pressed in directions Z. Namely, pressingand heating are simultaneously performed. Prepreg (insulation layers (20a, 30 a)) is cured through pressing and heating, and the members areadhered to each other. As a result, the laminate becomes integrated.Pressing and heating may be divided into multiple procedures. Also,heating and pressing may be conducted separately, but it is moreefficient if they are conducted at the same time. After thermalpressing, another round of heating for integration may be conducted.

Via holes (22 a) are formed in insulation layer (20 a) and via holes (32a) are formed in insulation layer (30 a) by using a laser, for example(see FIG. 12B). Then, desmearing is conducted if required.

After plating is formed on copper foils (1002, 1003) and in via holes(22 a, 32 a) by conducting copper panel plating, for example, conductivelayers on both surfaces are patterned using lithographic technology, forexample. Accordingly, via conductors (22, 32) and conductive layers (21,31) are formed as shown in FIG. 12B. Conductive layer 31 does not haveconductive patterns directly on (in direction Z) the regioncorresponding to groove section (R11). Each of via conductors (22, 32)is a filled conductor and is stacked directly on (in direction Z) viaconductor 12.

The same as in first buildup layers (insulation layers (20 a, 30 a),conductive layers (21, 31) and via conductors (22, 32)), second builduplayers (insulation layers (40 a, 50 a), conductive layers (41, 51) andvia conductors (42, 52)) and third buildup layers (insulation layers (60a, 70 a), conductive layers (61, 71) and via conductors (62, 72)) areformed in that order as shown in FIG. 13. However, prior to panelplating for forming conductive layers (61, 71), through holes (111 a)are formed. Accordingly, through-hole conductors 111 are formed on wallsurfaces of through holes (111 a) by the subsequent panel plating.

Conductive layers (51, 71) do not have conductive patterns directly on(in direction Z) the region corresponding to groove section (R11).Namely, there is no conductor (especially metal which easily reflectslaser light) directly on (in direction Z) the region corresponding togroove section (R11). In addition, each of via conductors (42, 52, 62,72) is a filled conductor and is stacked directly on (in direction Z)via conductor 12. They form a filled-stack structure.

As shown in FIG. 14, solder resist 81 having opening portions (81 a) andsolder resist 82 having opening portions (82 a) are formed respectivelyon insulation layers (70 a, 60 a). Conductive layers (71, 61) arecovered with solder resists (81, 82) except for predetermined spotspositioned at opening portions (81 a, 82 a) (pads (P1, P2), lands andthe like). Solder resists (81, 82) are formed by screen printing, spraycoating, roll coating, lamination or the like, for example. Pads (P1,P2) do not have anticorrosion layers (P13, P23) at this stage.

As described above, on first surface (F1) of wiring board 10 (oninsulation layer (10 a) and on conductive layer (11 a)), buildup section30 is formed with insulation layers (30 a, 50 a, 70 a) and solder resist81; and on second surface (F2) of wiring board 10 (on insulation layer(10 a) and on conductive layer (11 b)), buildup section 20 is formedwith insulation layers (20 a, 40 a, 60 a) and solder resist 82.

In step (S15) of FIG. 8, laser light is irradiated at groove section(R11) from the upper-layer side of buildup section 30.

In particular, as shown in FIG. 15A, for example, laser light isirradiated in the way that a rectangle is drawn, and part of buildupsection 30 is cut out from its surrounding portions. During that time,irradiation conditions of the laser light (such as intensity) areadjusted so that laser light reaches insulation layer (10 a) and groove(T1) is obtained having a required depth. The irradiation angle of thelaser light is set to be substantially perpendicular to first surface(F1) of wiring board 10, for example.

When changing irradiation spots of a laser, for example, it is preferredthat the object to be irradiated be fixed and the laser (in particularits aiming point) be moved; alternatively, it is preferred that thelaser (in particular its aiming point) be fixed and the object be moved.When the laser is moved, it is preferred to use a galvanometer mirror,for example.

In connection section (R13), multiple conductive patterns (101 c) areeach formed to cross groove (T1), and a laser is irradiated so thatportions of groove (T1) and conductive patterns (101 c) are alternatelypositioned as shown in FIG. 15B.

Here, groove (T1) is formed continuously except in connection section(R13). Furthermore, as shown in FIG. 15B, groove (T1) is formed so as tobe positioned between conductive patterns (101 c) made of metal (copperin the present embodiment) in connection section (R13). Since metaleasily reflects laser light, in the present embodiment, groove (T1) isformed by conducting maskless laser irradiation without pausing theirradiation at connection section (R13). However, when groove (T1) isformed intermittently in connection section (R13), it is preferred toset the intensity of the laser light less than when forming groove (T1)continuously (laser irradiation at portions except for connectionsection (R13)). In doing so, damage from laser irradiation to conductivepatterns (101 c) tends to be reduced. When irradiating laser light atconnection section (R13), it is preferred to precisely adjust theintensity (power adjustment) of the laser light.

In the present embodiment, the above laser irradiation is conductedmaskless without pausing irradiation. However, laser irradiation is notlimited to such. For example, laser light may be irradiated at theentire surface of the object using a shielding mask having openings onlyat irradiation spots; or laser light may be irradiated at portions to beirradiated without using a mask by pausing laser irradiation at portionsnot to be irradiated.

In addition, laser intensity (the amount of light) is preferred to beadjusted by pulse control. Specifically, for example, to modify laserintensity, the number of shots (irradiation number) is changed withoutchanging laser intensity per shot (one irradiation). Namely, if therequired laser intensity is not obtained with one shot, laser light isirradiated again at the same irradiation spot. If such a control methodis used, the throughput improves since time for modifying irradiationconditions is omitted. However, adjusting laser intensity is not limitedto the above, and any other method may be taken. For example,irradiation conditions may be determined for each irradiation spot,while the irradiation number is set constant (for example, one shot perone irradiation spot).

By the above laser irradiation, part of buildup section 30 (mask 1001and the portion above it) becomes separable while groove (T1) is formedin first surface (F1) of wiring board 10 (a main surface of insulationlayer (10 a) in particular) as shown in FIG. 16. Hereinafter, theseparable portion of buildup section 30 is referred to as cover portion1004. In the present embodiment, buildup section 30 is cut relativelyeasily by using a laser. Therefore, even if buildup section 30 is thick,or if buildup section 30 is formed as multilayer, groove (T1) tends tobe formed easily.

In step (S16) of FIG. 8, cover portion 1004 of buildup section 30 isremoved as shown in FIG. 17 by adding external force manually or usingother methods, for example. Accordingly, cavity (R1) is formed to have asurface (first surface F1) of insulation layer (10 a), where pads 101and groove (T1) are formed, as its bottom surface (F11). Also, groove(T1) is formed along wall surfaces (F12) of cavity (R1). In addition,pads 101 are positioned farther from wall surfaces (F12) than groove(T1) is.

In step (S17) of FIG. 8, anticorrosion layers (1013, P13, P23) (see FIG.5) made of Ni/Au film, for example, are formed on each exposed surface(such as a pad surface) through electrolytic plating, sputtering or thelike. Alternatively, anticorrosion layers (1013, P13, P23) made of anorganic solderability preservative may be formed through OSP treatment.Accordingly, pads 101 having anticorrosion layer 1013 on their surfacesand pads (P1, P2) respectively having anticorrosion layers (P13, P23) ontheir surfaces are formed as shown in FIGS. 1 and 5. Also, anticorrosionlayer 1013 (see FIG. 5) is formed partially on surfaces of conductivepatterns (101 c) (see FIG. 4), which are exposed in non-groove section(R12) of connection section (R13).

Wiring board 100 (FIGS. 1, 2) is completed by the steps described above.The manufacturing method according to the present embodiment ispreferable for manufacturing wiring board 100. An excellent wiring board100 is obtained at low cost according to such a manufacturing method.

So far, a wiring board and its manufacturing method according to anembodiment of the present invention have been described. However, thepresent invention is not limited to the above embodiment.

The shape of cavity (R1) is not limited to being substantiallyrectangular, and any other shape may be employed. For example, as shownin FIG. 18, cavity (R1) may be shaped to be substantially columnar.

Groove (T1) may be formed continuously without any break as shown inFIG. 18, for example. In such a case, non-groove section (R12) is aregion surrounded completely by ring-shaped groove (T1), which does nothave any break. In the example in FIG. 18, pads 101 are positioned innon-groove section (R12) (partial region of bottom surface (F11))surrounded by groove (T1).

Alternatively, as shown in FIG. 19, for example, non-groove section(R12) may be surrounded by groove (T1) which is formed with a brokenline. Such broken-line groove (T1) may be easily formed as follows:prior to laser irradiation for forming groove (T1), stoppers (101 d)(such as conductive patterns made of metal) that reflect a laser areformed in non-groove section (R12) between portions of groove (T1), forexample. Stoppers (101 d) may be such conductive patterns that do notform circuits, or may be conductive patterns that form circuits (such aspart of wiring). In the example in FIG. 19, non-groove section (R12)(stoppers 101 d) is formed to be a broken line. In addition, pads 101are positioned in non-groove section (R12) surrounded by groove (T1)(partial region of bottom surface (F11)).

In the above embodiment, groove (T1) is formed on bottom surface (F11)of cavity (R1) along substantially all wall surfaces (F12) of cavity(R1) (see FIG. 3A). However, the above embodiment is not limited tosuch; for example, as shown in FIG. 20, groove (T1) may be formed onlyalong part of wall surfaces (F12) of cavity (R1) (for example, along twosides). As in the case of the above broken-line groove (T1) (FIG. 19),such groove (T1) may also be easily formed, for example, by formingstoppers (101 d) (such as conductive patterns made of metal) in theregion where groove (T1) is not formed (non-groove section (R12)) priorto laser irradiation for forming groove (T1).

As shown in FIG. 20, pads 101 may be positioned outside the regionsurrounded by groove (T1) (the region shown by a broken line in FIG.20). In addition, as shown in FIG. 21, pads (101 b) electricallyconnected to conductive patterns (101 c) may be positioned in portionscorresponding to breaks in the ring that are formed by groove (T1). Insuch a case, without solder resist being formed between pads (101 b)(see FIG. 4), short circuiting caused by a solder bridge is prevented bygroove (T1) between pads (101 b).

The angle made by groove (T1) and conductive pattern (101 c) inconnection section (R13) is not limited to approximately 90 degrees; forexample, the angle may be acute or obtuse as shown in FIG. 22.

In the above embodiment, cavity (R1) penetrates through buildup section30. However, cavity (R1) is not limited to such and may also be anopening portion that does not penetrate through buildup section 30. Forexample, as shown in FIG. 23A, bottom surface (F11) of cavity (R1) maybe a main surface of insulation layer (30 a). Alternatively, as shown inFIG. 23B, for example, bottom surface (F11) of cavity (R1) may be a mainsurface of insulation layer (50 a). Yet alternatively, as shown in FIG.23A or 23B, pads 101 in cavity (R1) may be electrically connected to viaconductors (via conductors 122, 32 or via conductors 122, 32, 52) thatform a stack structure.

The shape of a cross section of groove (T1) (the cross sectionperpendicular to a longitudinal direction) is not limited to a rectanglewhose corners are at substantially right angles, and any other shape maybe employed. For example, the shape of a cross section of groove (T1)may be substantially trapezoidal having a width that decreases thedeeper it goes as shown in FIG. 24A, or may be substantially trapezoidalhaving a width that increases the deeper it goes as shown in FIG. 24B.Alternatively, the shape of a cross section of groove (T1) may be in asubstantially V shape as shown in FIG. 24C, or substantially in a Wshape as shown in FIG. 24D.

The planar shape of groove (T1) (on the X-Y plane) according to thepresent embodiment is not limited to a straight shape having asubstantially constant width, and any other shape may be employed. Forexample, as shown in FIG. 25, the planar shape of groove (T1) may be astraight shape having irregular width.

It is not always required for the entire side surface (all four sides)of electronic component 200 to be positioned in groove section (R11).For example, as shown in FIG. 26, it is possible for only part of theside surfaces of electronic component 200 (for example, three sides) tobe positioned in groove section (R11).

What is electrically connected to pads 101 is not limited to electroniccomponent 200 (FIG. 6A), and it may be another wiring board 300 as shownin FIG. 27, for example. In the example in FIG. 27, wiring board 300 isaccommodated in cavity (R1), and external connection terminals (300 a)of wiring board 300 are electrically connected to pads 101 throughsolder (300 b). Conductors in wiring board 300 are preferred to be setat a higher density than in wiring board 100 by, for example, arrangingfiner conductive patterns in each conductive layer or by decreasing thethickness of the interlayer insulation layer between conductive layers.

The method for mounting electronic component 200 or the like to beaccommodated in cavity (R1) is not limited to solder connections, butany other method may be employed. For example, other methods such as awire bonding connection or an ACF (anisotropic conductive film)connection may also be used.

Regarding other factors, the structure of wiring board 100 and the type,performance, dimensions, quality, shape, number of layers, positioningand so forth of the elements of such a structure, may be modified freelywithin a scope that does not deviate from the gist of the presentinvention.

For example, as shown in FIG. 28, a wiring board may be formed withoutfilled-stack structure “S”. In the example in FIG. 28, via conductors(22, 32, 42, 52, 62, 72) are positioned so that the terminal pitch ofpads 101 is widened toward the outer layer.

Also, as shown in FIG. 28, via conductors 12 are set to be conformalconductors, and insulative body (12 b) (such as resin) may be filled inthe inside. Alternatively, through-hole conductors may be used insteadof via conductors 12.

As shown in FIG. 29, for example, wiring board 100 may be a flex-rigidwiring board. In the example in FIG. 29, insulation layer (10 a) is madeof a flexible substrate.

As shown in FIG. 30, for example, wiring board 100 may be a single-sidedwiring board having conductive layers only on one side of the coresubstrate (insulation layer 10 a).

For example, via conductors (12, 22, 32, 42, 52, 62, 72) are not limitedto being filled conductors and may each be a conformal conductor.

The material for each conductive layer, via conductor and through-holeconductor is not limited to the above, and may be modified according tousage requirements or the like. For example, metal other than copper maybe used as their conductive material. Also, the material for eachinsulation layer is not limited to a specific type. However, as for theresin to form interlayer insulation layers, thermosetting resins orthermoplastic resins are preferred. As for thermosetting resins, forexample, other than epoxy resin, the following may be used: polyimide,BT resin, allyl polyphenylene ether resin (A-PPE resin), aramid resin orthe like. Also, as for thermoplastic resins, for example, liquid-crystalpolymer (LCP), PEEK resin, PTFE resin (fluoro resin) or the like may beused. Such materials are preferred to be selected according torequirements from the viewpoint of insulation, dielectric properties,tolerance to heat, mechanical features and so forth. In addition, theabove resins may contain additives such as a curing agent, a stabilizer,filler or the like. Alternatively, each conductive layer and eachinsulation layer may be formed with multiple layers made of differentmaterials.

The manufacturing steps of a wiring board are not limited to the orderand the contents shown in the flowchart in FIG. 8. The order and thecontents may be modified freely within a scope that does not deviatefrom the gist of the present invention. Also, unnecessary steps may beomitted depending upon usage or the like.

For example, instead of using a laser, dry or wet etching may beemployed for processing. When etching is employed for processing, theportions required to remain are preferred to be protected in advancewith resist or the like.

In addition, the method for forming each conductive layer is not limitedspecifically. For example, any method of the following or a combinationof two methods selected from among those may be used for formingconductive layers: panel-plating method, pattern-plating method,full-additive method, semi-additive (SAP) method, subtractive method,decal transfer method and tenting method.

The above embodiment and its modified example or the like may becombined freely. It is preferred to use a combination appropriate tousage requirements or the like.

A wiring board according to the first aspect of the present inventionhas the following: a cavity that opens toward one side; a groove formedon the bottom surface of the cavity and along the wall surfaces of thecavity; and a pad formed on the bottom surface of the cavity in aposition farther from the wall surfaces than the groove is.

A method for manufacturing a wiring board according to the second aspectof the present invention includes the following: preparing an insulationlayer where a conductive layer containing a pad is formed on a mainsurface; on the insulation layer and on the conductive layer, forming abuildup section made with one or two or more other insulation layers; byirradiating laser light from the upper-layer side of the buildupsection, setting a portion of the buildup section to be separable whileforming a groove in the insulation layer; and by removing the separableportion of the buildup section, forming a cavity to have a surface ofthe insulation layer, where the pads and the groove are formed, as itsbottom surface.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1-12. (canceled)
 13. A method for manufacturing a wiring board, comprising: preparing an insulation layer having a conductive layer comprising a pad formed on a surface of the insulation layer; covering the pad with a mask layer which is separable from the insulation layer and is substantially corresponding to a bottom surface of a cavity portion; forming on the insulation layer, the conductive layer and the mask layer a buildup structure comprising a plurality of insulation layers; irradiating laser on a surface of the buildup structure on an opposite side of the insulation layer substantially along a shape of the mask layer such that the laser forms a separable portion including the mask layer in the buildup structure and a groove portion in the insulation layer substantially along the shape of the mask layer; and removing the separable portion formed in the buildup structure such that the cavity portion having the groove portion on the surface of the insulation layer is formed and the pad is exposed on the bottom surface of the cavity portion in a position farther from the wall surface of the cavity portion than the groove portion.
 14. The method for manufacturing a wiring board according to claim 13, wherein the conductive layer includes a conductive pattern electrically connected to the pad, and the groove portion is crossing a portion of the conductive pattern.
 15. The method for manufacturing a wiring board according to claim 14, wherein the laser is set to an intensity which is sufficiently low such that the groove portion is formed intermittently.
 16. The method for manufacturing a wiring board according to claim 14, wherein the buildup structure comprises a laminated structure in which the plurality of insulation layers are laminated, and the cavity portion of the board structure is formed in the laminated structure.
 17. The method for manufacturing a wiring board according to claim 14, wherein the insulation layer of the board structure is a rigid substrate having a core material, and the groove portion of the cavity portion is formed in the rigid substrate.
 18. A method for manufacturing a wiring board, comprising: forming a board structure comprising an insulation layer, a buildup structure formed on the insulation layer and a pad formed in the board structure, the buildup structure comprising a plurality of insulation layers; and forming a cavity portion in the board structure such that the cavity portion has an opening on a surface of the buildup structure on an opposite side of the insulation layer, the cavity portion is extending through at least one of the insulation layers in the buildup structure, the cavity portion has a groove portion formed on a bottom surface of the cavity portion along a wall surface of the cavity portion, and the pad formed in the board structure is exposed on the bottom surface of the cavity portion in a position farther from the wall surface of the cavity portion than the groove portion, wherein the forming of the board structure comprises covering the pad with a separable mask layer which is substantially corresponding to the bottom surface of the cavity portion, and the forming of the cavity portion in the board structure comprises irradiating laser on the surface of the buildup structure substantially along a shape of the separable mask layer such that the laser forms a separable portion including the separable mask layer in the buildup structure and a groove portion in the bottom surface of the cavity portion substantially along the shape of the mask layer and removing the separable portion formed in the buildup structure such that the cavity portion having the groove portion is formed and the pad is exposed in the cavity portion formed in the board structure.
 19. The method for manufacturing a wiring board according to claim 18, wherein the conductive layer includes a conductive pattern electrically connected to the pad, and the groove portion is crossing a portion of the conductive pattern.
 20. The method for manufacturing a wiring board according to claim 18, wherein the laser is set to an intensity which is sufficiently low such that the groove portion is formed intermittently.
 21. The method for manufacturing a wiring board according to claim 13, wherein the groove portion is formed such that the groove portion surrounds a partial region on the bottom surface of the cavity portion along the wall surface of the cavity portion, and the pad is positioned in the partial region on the bottom surface of the cavity portion.
 22. The method for manufacturing a wiring board according to claim 13, further comprising forming a solder resist on a portion of the bottom surface of the cavity portion where the groove portion is not formed such that the solder resist has an opening exposing the pad.
 23. The method for manufacturing a wiring board according to claim 13, wherein the pad has an anticorrosion layer forming a surface of the pad.
 24. The method for manufacturing a wiring board according to claim 23, further comprising forming a solder structure on the anticorrosion layer of the pad.
 25. The method for manufacturing a wiring board according to claim 23, further comprising forming a plurality of pads on the surface of the buildup structure outside the cavity portion, wherein the pads on the surface of the buildup structure have anticorrosion layers on surfaces of the pads, and the anticorrosion layer on the pad inside the cavity portion comprises a same anticorrosion material as the anticorrosion layers on the pads on the surface of the buildup structure.
 26. The method for manufacturing a wiring board according to claim 18, wherein the groove portion is formed such that the groove portion surrounds a partial region on the bottom surface of the cavity portion along the wall surface of the cavity portion, and the pad is positioned in the partial region on the bottom surface of the cavity portion.
 27. The method for manufacturing a wiring board according to claim 18, further comprising forming a solder resist on a portion of the bottom surface of the cavity portion where the groove portion is not formed such that the solder resist has an opening exposing the pad.
 28. The method for manufacturing a wiring board according to claim 18, wherein the pad has an anticorrosion layer forming a surface of the pad.
 29. The method for manufacturing a wiring board according to claim 28, further comprising forming a solder structure on the anticorrosion layer of the pad.
 30. The method for manufacturing a wiring board according to claim 28, further comprising forming a plurality of pads on the surface of the buildup structure outside the cavity portion, wherein the pads on the surface of the buildup structure have anticorrosion layers on surfaces of the pads, and the anticorrosion layer on the pad inside the cavity portion comprises a same anticorrosion material as the anticorrosion layers on the pads on the surface of the buildup structure.
 31. The method for manufacturing a wiring board according to claim 18, wherein the buildup structure comprises a laminated structure in which the plurality of insulation layers are laminated, and the cavity portion of the board structure is formed in the laminated structure.
 32. The method for manufacturing a wiring board according to claim 18, wherein one of the insulation layers in the buildup structure has a surface portion forming the bottom surface of the cavity portion, and the groove portion of the cavity portion is formed in the one of the insulation layers in the buildup structure such that the groove portion of the cavity portion does not penetrate through the one of the insulation layers in the buildup structure. 